[Keyboard] Add Mechlovin9 rev.3 (#20119)

Co-authored-by: jack <0x6a73@protonmail.com>

keyboards/mechlovin/mechlovin9/rev3/info.json

@@ -0,0 +1,22 @@
+{
+    "keyboard_name": "Mechlovin9 Rev3",
+    "processor": "STM32F103",
+    "bootloader": "stm32duino",
+    "usb": {
+        "pid": "0x6509",
+        "device_version": "0.0.3"
+    },
+    "features": {
+        "backlight": false
+    },
+    "bootmagic": {
+        "matrix": [0, 13]
+    },
+    "matrix_pins": {
+        "rows": ["B12", "B13", "B14", "B15", "A1"],
+        "cols": ["B11", "B10", "B2", "B1", "B0", "A6", "A5", "A4", "A3", "C13", "B7", "B6", "B5", "B4", "B3"]
+    },
+    "indicators": {
+        "caps_lock": "B9"
+    }
+}